Diminished expression of β2-GPI is associated with a reduced ability to mitigate complement activation in anti-GPIIb/IIIa-mediated immune thrombocytopenia

Complement activation negatively affects the platelet response to thrombopoietin receptor agonists in patients with immune thrombocytopenia: a prospective cohort study

Increased platelet destruction is central in the pathogenesis of immune thrombocytopenia. However, impaired platelet production is also relevant and its significance underlies the rationale for treatment with thrombopoietin receptor agonists (TPO-RAs). Previous studies have associated enhanced complement activation with increased disease severity. Additionally, treatment refractoriness has been demonstrated to resolve by the administration of complement-targeted therapeutics in a subset of patients. The association between complement activation and the platelet response to TPO-RA therapy has previously not been investigated. In this study, blood samples from patients with immune thrombocytopenia (n = 15) were prospectively collected before and two, six and 12 weeks after the initiation of TPO-RA therapy. Plasma levels of complement degradation product C4d and soluble terminal complement complexes were assessed. Patients with significantly elevated baseline levels of terminal complement complexes exhibited more often an inadequate platelet response (p = .04), were exclusively subjected to rescue therapy with intravenous immunoglobulin (p = .02), and did not respond with a significant platelet count increase during the study period. C4d showed a significant (p = .01) ability to distinguish samples with significant terminal complement activation, implying engagement of the classical complement pathway. In conclusion, elevated levels of complement biomarkers were associated with a worse TPO-RA treatment response. Larger studies are needed to confirm these results. Biomarkers of complement activation may prove valuable as a prognostic tool to predict which patients that potentially could benefit from complement-inhibiting therapy in the future.

Involvement of the complement system in immune thrombocytopenia: review of the literature

Immune thrombocytopenia (ITP) is a thrombocytopenic condition induced by autoimmune mechanisms and includes secondary ITP with underlying diseases such as connective tissue diseases (CTD). In recent years, it has been elucidated that the subsets of the ITP are associated with complement abnormalities but much remains unclear. To perform a literature review and identify the characteristics of complement abnormalities in ITP. PUBMED was used to collect the literature published up to June 2022 related to ITP and complement abnormalities. Primary and secondary ITP (CTD-related) were examined. Out of the collected articles, 17 were extracted. Eight articles were related to primary ITP (pITP) and 9 to CTD-related ITP. Analysis of the literature revealed that the ITP severity was inversely correlated with serum C3, C4 levels in both ITP subgroups. In pITP, a wide range of complement abnormalities was reported, including abnormalities of initial proteins, complement regulatory proteins, or the end products. In CTD-related ITP, reported complement abnormalities were limited to the initial proteins. Activation of the early complement system, mainly through activation of C3 and its precursor protein C4, was reported for both ITPs. On the other hand, more extensive complement activation has been reported in pITP.

Therapeutic potential of MSCs and MSC-derived extracellular vesicles in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired autoimmune disease involving a variety of immune cells and factors. Despite being a benign disease, it is still considered incurable due to its complex pathogenesis. Mesenchymal stem cells (MSCs), with low immunogenicity, pluripotent differentiation, and immunomodulatory ability, are widely used in a variety of autoimmune diseases. In recent years, impaired bone marrow mesenchymal stem cells (BMMSCs) were found to play an important role in the pathogenesis of ITP; and the therapeutic role of MSCs in ITP has also been supported by increasing evidence with encouraging efficacy. MSCs hold promise as a new approach to treat or even cure refractory ITP. Extracellular vesicles (EVs), as novel carriers in the "paracrine" mechanism of MSCs, are the focus of MSCs. Encouragingly, several studies suggested that EVs may perform similar functions as MSCs to treat ITP. This review summarized the role of MSCs in the pathophysiology and treatment of ITP.

Novel Biomarkers for Diagnosis and Monitoring of Immune Thrombocytopenia

Lower-than-normal platelet counts are a hallmark of the acquired autoimmune illness known as immune thrombocytopenia, which can affect both adults and children. Immune thrombocytopenia patients' care has evolved significantly in recent years, but the disease's diagnosis has not, and it is still only clinically achievable with the elimination of other causes of thrombocytopenia. The lack of a valid biomarker or gold-standard diagnostic test, despite ongoing efforts to find one, adds to the high rate of disease misdiagnosis. However, in recent years, several studies have helped to elucidate a number of features of the disease's etiology, highlighting how the platelet loss is not only caused by an increase in peripheral platelet destruction but also involves a number of humoral and cellular immune system effectors. This made it possible to identify the role of immune-activating substances such cytokines and chemokines, complement, non-coding genetic material, the microbiome, and gene mutations. Furthermore, platelet and megakaryocyte immaturity indices have been emphasized as new disease markers, and prognostic signs and responses to particular types of therapy have been suggested. Our review's goal was to compile information from the literature on novel immune thrombocytopenia biomarkers, markers that will help us improve the management of these patients.

All-trans retinoic acid protects mesenchymal stem cells from immune thrombocytopenia by regulating the complement-interleukin-1β loop

Enhanced peripheral complement activation has long been considered as one of the major pathogenic elements of immune thrombocytopenia. A dysfunctional bone marrow microenvironment, especially with regards to mesenchymal stem cells, has been observed in patients with immune thrombocytopenia. However, the potential role of the complement system in the dysfunctional bone marrow microenvironment remains poorly understood. In this study, bone marrow samples from patients with immune thrombocytopenia were divided into two groups based on whether or not complement components were deposited on the surfaces of their mesenchymal stem cells. The mesenchymal cells from the group with complement deposition were less numerous, dysfunctional, had a reduced capacity to proliferate, and showed increased apoptosis as well as abnormal secretion of interleukin-1β and C-X-C motif chemokine ligand 12. In vitro treatment with all-trans retinoic acid increased the number and improved the function of the complement-positive bone marrow mesenchymal stem cells by upregulating DNA hypermethylation of the interleukin-1β promoter. In vivo studies showed that all-trans retinoic acid could rescue the impaired mesenchymal stem cells to support the thrombopoietic niche in both patients with immune thrombocytopenia and a murine model of this disease. Taken together, these results indicate that impairment of mesenchymal stem cells, mediated by the complement-interleukin-1β loop, plays a role in the pathogenesis of immune thrombocytopenia. All-trans retinoic acid represents a promising therapeutic approach in patients with immune thrombocytopenia through its effect of repairing mesenchymal stem cell impairment.

Rituximab in the treatment of immune thrombocytopenia: what is the role of this agent in 2019?

The use of rituximab for the treatment of immune thrombocytopenia was greeted enthusiastically: it led to up to 60% response rates, making it, nearly 20 years ago, the main alternative to splenectomy, with far fewer side effects. However, long-term follow-up data showed that only 20-30% of patients maintained the remission. No significant changes have been registered using different dose schedules and timing of administration, while the combination with other drugs seemed promising. Higher response rates have been observed in young women before the chronic phase, but apart from that, other clinical factors or biomarkers predictive of response are still lacking. In this review we examine the historical and current role of rituximab in the management of immune thrombocytopenia, 20 years after its first use for the treatment of autoimmune diseases.

Opposite Profiles of Complement in Antiphospholipid Syndrome (APS) and Systemic Lupus Erythematosus (SLE) Among Patients With Antiphospholipid Antibodies (aPL)

APS is the association of antiphospholipid antibodies (aPL) with thromboses and/or recurrent pregnancy loss (RPL). Among patients with SLE, one-third have aPL and 10–15% have a manifestation of secondary APS. Animal studies suggested that complement activation plays an important role in the pathogenesis of thrombosis and pregnancy loss in APS. We performed a cross-sectional study on complement proteins and genes in 525 patients with aPL. Among them, 237 experienced thromboses and 293 had SLE; 111 had both SLE and thromboses, and 106 had neither SLE nor thrombosis. Complement protein levels were determined by radial immunodiffusion for C4, C3 and factor H; and by functional ELISA for mannan binding lectin (MBL). Total C4, C4A and C4B gene copy numbers (GCN) were measured by TaqMan-based realtime PCR. Two to six copies of C4 genes are frequently present in a diploid genome, and each copy may code for an acidic C4A or a basic C4B protein. We observed significantly (a) higher protein levels of total C4, C4A, C4B, C3, and anticardiolipin (ACLA) IgG, (b) increased frequencies of lupus anticoagulant and males, and (c) decreased levels of complement factor H, MBL and ACLA-IgM among patients with thrombosis than those without thrombosis (N = 288). We also observed significantly lower GCNs of total C4 and C4A among aPL-positive patients with both SLE and thrombosis than others. By contrast, aPL-positive subjects with SLE had significantly reduced protein levels of C3, total C4, C4A, C4B and ACLA-IgG, and higher frequency of females than those without SLE. Patients with thrombosis but without SLE (N = 126), and patients with SLE but without thrombosis (N = 182) had the greatest differences in mean protein levels of C3 (p = 2.6 × 10⁻⁶), C4 (p = 2.2 × 10⁻⁹) and ACLA-IgG (p = 1.2 × 10⁻⁵). RPL occurred in 23.7% of female patients and thrombotic SLE patients had the highest frequency of RPL (41.0%; p = 3.8 × 10⁻¹⁰). Compared with non-RPL females, RPL had significantly higher frequency of thrombosis and elevated C4 protein levels. Female patients with homozygous C4A deficiency all experienced RPL (p = 0.0001) but the opposite was true for patients with homozygous C4B deficiency (p = 0.017). These results provide new insights and biomarkers for diagnosis and management of APS and SLE.

Evaluation of EC50 of factor VIII as predictor of prophylaxis efficacy in patients with severe haemophilia A

Trough factor (F) VIII level is a not reliable bleeding risk indicator to predict prophylaxis efficacy in severe haemophilia A (SHA), therefore, accurate biomarkers are much needed. Thrombelastography (TEG) monitors both thrombin and clot formation addressing the global haemostatic status but its usefulness to tailor prophylaxis in haemophilia has been poorly evaluated. In this study, correspondence between individual pharmacodynamic/pharmacokinetic profile of FVIII and joint condition, physical activity and bleeding phenotype of SHA patients under prophylactic treatment was assessed. Nineteen SHA patients < 18 years old on long-term prophylaxis treatment with FVIII were studied in an observational cross-sectional study. Whole blood was withdrawn before FVIII administration and at five time-points after infusion for a TEG-based pharmacodynamic- and pharmacokinetic-study. Type of prophylaxis and joint condition at inclusion and physical activity as well as onset of treated spontaneous bleeding events in the previous two years were retrospectively assessed. Six patients had suffered at least one treated spontaneous bleeding event and were named as "bleeders". The rest were named as "non-bleeders". Only the half maximal effective concentration of FVIII (FVIII-EC50) for TEG parameters R-time, K-time and α-angle correlated with the bleeding phenotype being significantly higher in bleeders suggestive of a poorer response to FVIII. Poorer joint condition, trough FVIII levels or type of prophylaxis were not definitive predicting variables of bleeding phenotype. In conclusion, this study reveals FVIII-EC50 for the first time as a valuable biomarker to anticipate individual efficacy of prophylaxis in SHA.